Submitted on: 16 December 2017.
Revised on: 11 January 2018.
Accepted on: 07 March 2018.
___________________International Journal of Dynamical Systems and Differential Equations
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Submitted on: 04 March 2004.
Revised on: 23 April 2004.
Accepted on: 08 May 2004.
___________________International Journal of Dynamical Systems and Differential Equations
Submitted on: 28 November 2005.
Revised on: 05 March 2006.
Accepted on: 29 March 2006.
___________________International Journal of Dynamical Systems and Differential Equations